Balance
Use a balance with mystery weights on it to learn about balancing equations and isolating variables is invaluable as you can show them that you need to do the same thing to both sides. This strategy is particularly useful with the intermediate grades as they have just started developing their abstract thinking abilities.
This is a good set of pattern block ideas for grades 7 & 8 developed by UOIT pre-service students (2010)
Linking Cubes Ideas
This is a good set of linking cube ideas for grades 7 & 8 developed by UOIT pre-service students (2010)
Video
This is proof that students will not rely on manipulatives if they become really comfortable with the tool:
http://www.youtube.com/watch?v=wIiDomlEjJw
ps Abacus' are SO cool!
Balance
Use a balance with mystery weights on it to learn about balancing equations and isolating variables is invaluable as you can show them that you need to do the same thing to both sides. This strategy is particularly useful with the intermediate grades as they have just started developing their abstract thinking abilities.